Exhibit 5.1

Wilson Sonsini Goodrich & Rosati Professional Corporation   650 Page Mill Road Palo Alto, CA 94304   O: (650) 493-9300 F: (650) 493-6811

November 13, 2023

Allakos Inc.

825 Industrial Road, Suite 500

San Carlos, CA 94070

Re: Registration Statement on Form S-3

Ladies and Gentlemen:

At your request, we have examined the Registration Statement on Form S-3 (the “Registration Statement”), filed by Allakos Inc., a Delaware corporation (the “Company”), with the Securities and Exchange Commission (the “Commission”) in connection with the registration pursuant to the Securities Act of 1933, as amended (the “Act”), of the Securities (as defined below).

The Registration Statement relates to the proposed issuance and sale by the Company, from time to time, pursuant to Rule 415 under the Act, as set forth in the Registration Statement, the prospectus contained therein (the “Prospectus”) and the supplements to the prospectus referred to therein (each a “Prospectus Supplement”), of up to an aggregate offering price of $250,000,000, or the equivalent thereof, of shares of the Company’s common stock, $0.001 par value per share (the “Common Stock”) (the Common Stock are referred to herein as the “Securities”).

The Securities are to be sold from time to time as set forth in the Registration Statement, the Prospectus contained therein and the Prospectus Supplements. The Securities are to be sold pursuant to a purchase, underwriting or similar agreement in substantially the form to be filed under a Current Report on Form 8-K.

We have examined instruments, documents, certificates and records that we have deemed relevant and necessary for the basis of our opinions hereinafter expressed. In such examination, we have assumed: (a) the authenticity of original documents and the genuineness of all signatures; (b) the conformity to the originals of all documents submitted to us as copies; (c) the truth, accuracy and completeness of the information, representations and warranties contained in the instruments, documents, certificates and records we have reviewed; (d) that the Registration Statement, and any amendments thereto (including post-effective amendments), will have become effective under the Act; (e) that a Prospectus Supplement will have been filed with the Commission describing the Securities offered thereby; (f) that the Securities will be issued and sold in compliance with applicable U.S. federal and state securities laws and in the manner stated in the Registration Statement and the applicable Prospectus Supplement; (g) that a definitive purchase, underwriting or similar agreement with respect to any Securities offered will have been duly authorized and validly executed and delivered by the Company and the other parties thereto; (h) that any Securities issuable upon conversion, exchange, redemption or exercise of any Securities being offered will be duly authorized, created and, if appropriate, reserved for issuance upon such conversion, exchange, redemption or exercise; (i) with respect to shares of Common Stock, that there will be sufficient shares of Common Stock authorized under the Company’s organizational documents that are not otherwise reserved for issuance; and (j) the legal capacity of all natural persons. As to any facts material to the opinions expressed herein that were not independently established or verified, we have relied upon oral or written statements and representations of officers and other representatives of the Company. The term “Board” means the Board of Directors of the Company or a duly constituted and acting committee thereof.

AUSTIN        BEIJING        BOSTON         BOULDER        BRUSSELS        HONG KONG        LONDON        LOS ANGELES        NEW YORK        PALO ALTO

SALT LAKE CITY        SAN DIEGO        SAN FRANCISCO        SEATTLE        SHANGHAI        WASHINGTON, DC        WILMINGTON, DE

Allakos Inc.

November 13, 2023

Page  2

Based on such examination, we are of the opinion that:

1.        With respect to the shares of Common Stock, when: (a) the Board has taken all necessary corporate action to approve the issuance and the terms of the offering of the shares of Common Stock and related matters; and (b) the shares of Common Stock have been duly delivered in accordance with the applicable definitive purchase, underwriting or similar agreement approved by the Board, for the consideration approved by the Board, then the shares of Common Stock will be validly issued, fully paid and nonassessable.

Our opinion that any document is legal, valid and binding is qualified as to:

(a)        limitations imposed by bankruptcy, insolvency, reorganization, arrangement, fraudulent transfer, moratorium or other similar laws relating to or affecting the rights of creditors generally;

(b)        rights to indemnification and contribution, which may be limited by applicable law or equitable principles; and

(c)        the effect of general principles of equity, including without limitation concepts of materiality, reasonableness, good faith and fair dealing, and the possible unavailability of specific performance or injunctive relief, whether considered in a proceeding in equity or at law.

We express no opinion as to the laws of any other jurisdiction, other than the federal laws of the United States of America and the General Corporation Law of the State of Delaware.

* * *

Allakos Inc.

November 13, 2023

Page  3

We hereby consent to the filing of this opinion as an exhibit to the above-referenced Registration Statement and to the use of our name wherever it appears in the Registration Statement, the Prospectus, any Prospectus Supplement, and in any amendment or supplement thereto. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission thereunder.

Very truly yours,

/s/ Wilson Sonsini Goodrich & Rosati, P.C.

WILSON SONSINI GOODRICH & ROSATI

Professional Corporation